Disk drives are widely used in computers and data processing systems for storing information in digital form. These disk drives commonly use one or more rotating storage disks to store data in digital form. Each storage disk typically includes a data storage surface on each side of the storage disk. These storage surfaces are divided into a plurality of narrow, annular, regions of different radii, commonly referred to as “tracks”. Typically, a head stack assembly including a positioner and an E-block are used to position a data transducer of a transducer assembly proximate each data storage surface of each storage disk. With these systems, the accurate and stable positioning of the data transducer is critical to the accurate transfer and/or retrieval of information from the rotating storage disks.
The data transducer transfers information to and from the storage disk. The transducer assembly also includes a load beam and a suspension for supporting the data transducer near the storage surface. The load beam is somewhat similar to a cantilevering spring element and applies a downward force on the data transducer.
The need for increased storage capacity has led to the use of disks having increased track density and decreased track pitch, i.e., more tracks per inch. As the tracks per inch increase, the ability to maintain the data transducer on a particular target track becomes more difficult.
The inaccurate positioning of the data transducer relative to the tracks on the rotating disks is commonly referred to as “track mis-registration.” Track mis-registration leads to errors or delays in the transfer of data. Mechanical phenomena that contribute to track mis-registration include: (i) non-repeatable spindle runout, i.e. bearing defects, ball cage, etc.; (ii) repeatable spindle runout, i.e. imbalance caused by disk shift, etc.; (iii) disk vibration modes; (iv) structure vibration modes, i.e. rotor, coil, bearings, base, etc.; (v) rotor bearing non-linear friction; (vi) windage disturbance (vibrations) of the head stack assembly; and (vii) externally applied shock and vibration.
Keeping the data transducer positioned on the target track with all of these disturbances, while at the same time increasing the tracks per inch, requires that the servo band-width of the positioner be increased. Over the past several years the structures of the disk drive have become smaller and have higher resonance characteristics. Thus, increasing the servo band-width of the positioner has proven to be increasingly difficult.
One attempt to increase servo band-width and minimize track mis-registration includes securing two piezoelectric motors to the load beam. More specifically, in this design, a hinge section is added to the load beam. The hinge section allows the load beam to flex in the tracking direction. The two piezoelectric motors are attached across the hinge section. When the piezo electric motors are energized, the load beam, and thus the data transducer, can be moved back and forth in the tracking direction.
However, material must be removed from the load beam to create the hinge section. This reduces the strength of the load beam. Further, the piezoelectric motors, which are attached across the hinge section, become a significant portion of the load beam structure and provide a substantial portion of the strength of the load beam.
Unfortunately, shock loads and vibration to the disk drive can cause significant bending of the load beam. Further, the load beam is subjected to repeated and significant bending in a ramp load/unload type disk drive. In this design, the piezoelectric motors attached to the load beam are placed in a shear mode when a significant bending force is applied to the load beam. Typically, the piezoelectric motors are made from a ceramic material which is very brittle and subject to stress cracking when subjected to bending actions. Thus, shock loads and vibration to the disk drive can cause the piezoelectric motors to function improperly and/or fail.
Additionally, because the piezoelectric motors are placed in a portion of the load beam that is very sensitive to the function and dynamics of the load beam, small changes in load beam stiffness may result in head gram load loss. Further, the motors influence the geometry, mass and center of gravity of the head stack assembly. This can adversely affect the resonance characteristics of the head stack assembly.
In light of the above, it is an object of the present invention to provide a head stack assembly having a higher servo-band width. Another object of the present invention is to add a fine positioner to a traditional head stack assembly with minimal changes to the design of the head stack assembly. Still another object of the present invention is to minimize track mis-registration. Yet another object of the present invention is to increase the reliability of the head stack assembly. Still another object is to provide a high-density disk drive.